The following Background of the Invention is intended to aid the reader in understanding the invention and is not admitted to be prior art.
In recent years, medical care has changed dramatically, from primarily using clinical laboratory analysis of samples to rapid point of care testing in the doctor's office or at the patient's bedside. Disposable enzyme biosensors are frequently used to perform these rapid tests. Taking glucose testing as an example, in-home testing by the patient is now commonplace and a necessity for proper disease management. To conduct an in-home test using a glucose biosensor, the diabetic patient lances the finger to withdraw a small amount of blood. The patient applies the blood to the biosensor test strip and within a few seconds the meter accompanying the biosensor records electrical data from the biosensor and calculates the glucose concentration in the patient's blood. This information is used to make decisions about when and how much insulin to administer.
In spite of the advances achieved in rapid and accurate measurement of metabolites, patient compliance remains a significant problem due to the pain associated with blood withdrawal. To reduce pain and increase patient compliance, new lancet devices that obtain blood from the forearm or thigh are now in use. These lancet devices cause less pain because there are fewer nerve endings in these locations of the body. However, there are also fewer surface blood vessels, which make it difficult to obtain enough blood for the test. In general, patients find that if the lancet device is set for less pain, less blood is obtained. This is a problem because prior art biosensors require several microliters of blood to correctly fill the capillary channel and function. If the volume of sample is too low, the capillary channel will not fill properly. The test will either not work or will give inaccurate results. Then, the patient will have to throw the improperly filled test strip away, and start over. The patient will have to stick himself with the lancet at least one more time and use a second test strip. This situation is very difficult and upsetting for some patients and reduces their compliance in blood monitoring. Consequently, these patients have difficulty monitoring and correctly treating their disease.
Several examples of biosensors are available. For example, U.S. Pat. Nos. 5,120,420 and 5,320,732 to Nankai, U.S. Pat. No. 5,141,868 to Shanks and U.S. patent application 2003/0196894 to Cai disclose disposable glucose biosensors. These biosensors are constructed of two plastic layers laminated to spacers and thereby held together. This structure forms a vented capillary channel that draws an applied sample into the interior and onto a test area. Venting is required for the capillary channel to function properly. When the sample flows into the channel by capillary flow, the sample comes into contact with an enzyme layer and electrodes, which detect and optionally measure an analyte in the sample.
Accordingly, there is a persistent need in the art for biosensors and methods that provide for improved sample application and measuring properties.